Cognitive dissonance is a perceived inconsistency between two cognitions in which the person believes one thing but then acts in a different way from what they believed. Or holds other beliefs which conflct with the first.
I should point out that "cognitive dissonance" is a term with a much wider field of applicability than the mating habits of particular people. The definition given above is more or less accurate. And we all suffer from cognitive dissonance on some level.